1. Field of the Invention
The present invention relates to a thin film transistor, a method for manufacturing the thin film transistor, and a display device to which the thin film transistor is applied.
2. Description of the Related Art
As one type of field-effect transistor, a thin film transistor whose channel formation region is formed using a semiconductor layer that is formed over a substrate having an insulating surface is known. Techniques for using amorphous silicon, microcrystalline silicon, and polycrystalline silicon for semiconductor layers in thin film transistors have been disclosed (see References 1 to 5). A typical application of thin film transistors is a liquid crystal television device, in which thin film transistors have been put to practical use as a switching transistor for each pixel that constitutes a display screen.